Circuit arrangement for ultrasonic burglar security systems oper

Details Circuit arrangement for ultrasonic burglar security systems oper Circuit arrangement for ultrasonic burglar security systems oper

1978-04-13

1980-04-15

Tubbesing, T. H.

Communications, electrical: acoustic wave systems and devices

Echo systems

Presence or movement only detection

343 5PD, G01S 966

Patent

active

041986180

ABSTRACT:
A circuit arrangement for an ultrasonic burglar security system operates in accordance with the Doppler principle and comprises a transmitting transducer which is fed from an oscillator with an ac voltage and continuously transmits ultrasonic radiation during operation, a receiving transducer and a receiving circuit connected thereto and having an analysis circuit and a phase detector which continuously compares the signal received by the receiving transducer with the oscillator ac voltage to form a detection signal which is dependent upon the mutual phase angle. The detection signal is fed to the analysis circuit which responds to the ac component thereof. The circuit arrangement includes a phase-locked loop (PLL) which includes a further detector, a low-pass filter following the phase detector and an oscillator. The oscillator has its frequency controlled at a control input and may be formed as a voltage controlled oscillator (VCO). The cut-off frequency of the low-pass filter is designed to be such that only signals which can pass fundamentally without reduction are those whose frequency is lower than a critical frequency F.sub.c =c/E, where c is the speed of sound of the ultrasonic radiation in the area and E is the path of the ultrasonic radiation from the transmitting transducer to a reflective object located in the predetermined maximum range and back to the receiving transducer.

REFERENCES:
patent: 3202960 (1965-08-01), Galbraith
patent: 3631849 (1972-01-01), Norris
patent: 4017684 (1978-08-01), Watson, Jr.

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